1. Field of the Invention
The present invention relates to an antenna device for use in a near field radio communication system, and an electronic device including the antenna device.
2. Description of the Related Art
In an RFID in the HF band, such as NFC (Near Field Communication), that is mounted on a mobile terminal, a coil antenna that magnetically couples with a communication counterpart-side antenna is used.
For example, Japanese Unexamined Patent Application Publication No. 2003-16409 discloses a mobile device that includes an RFID tag and in which a coil antenna of the RFID tag is disposed within a case of the mobile device.
In Japanese Unexamined Patent Application Publication No. 2003-16409, the coil antenna is disposed within the case of the device, but Japanese Unexamined Patent Application Publication No. 2003-16409 does not disclose a connection structure with a wiring conductor provided on a printed wiring board.
To provide a coil antenna within a mobile electronic device, it makes sense to configure the coil antenna as a surface-mountable component and mount the coil antenna on the printed wiring board similarly to other electronic components.
However, as a result of research performed by the inventor of the present invention, it has been discovered that unnecessary coupling between the wiring conductor and the coil antenna becomes a problem or the wiring conductor has an effect on the characteristics of the antenna device. For example, a problem has been discovered that due to unnecessary coupling between the wiring conductor and the coil antenna or the inductance of the wiring conductor, the characteristics of the coil antenna as a single component and the characteristics of the coil antenna in a state where the coil antenna is mounted on the board may differ greatly from each other.
The problem of unnecessary coupling between the wiring conductor and the coil antenna or the inductance of the wiring conductor has also not been considered in Japanese Unexamined Patent Application Publication No. 2003-16409 and has not been recognized in the relevant technical field.